1. Field of the Invention
The invention relates to breathing tubes and in particular to heated breathing tubes for use in delivering breathing gases to a patient. In a more particular aspect the invention relates to a heated inspiratory breathing tube for neonatal breathing applications.
2. Description of the Related Art
In assisted breathing, gases having elevated levels of relative humidity are supplied to, (and returned from) a patient (via a patient interface) through flexible breathing tubes of a relatively restricted size typically between a range of approximately 3 mm to 30 mm diameter (range covering both neonatal and adult applications). Such breathing tubes are ideally very light, resistant to kinking or pinching but also very flexible to ensure the greatest performance and level of comfort for the patient. The light weight of a breathing tube is very important to reduce any forces applied to the patient interface by the weight of the tube.
Various patient interface components may be used as appropriate for the type of breathing assistance required for different patients. For example, nasal cannula, nasal prongs, oral nasal masks, ET tubes, full face masks, or nasal pillows etc. The suitable choice will depend on various parameters associated with the type of treatment, such as the required gases flow rate, supplemental gases delivery, interface seal requirements, and/or therapy pressure for example.
Nasal cannulae may be used for example, in circumstances where a patient is breathing normally, or requires supplementary gases such as oxygen. These devices are typically supplied by a double entry lumen of small diameter (2-3 mm range) that attaches to a breathing tube. The small lumen tubes supply both sides of the nasal cannula and provide even airflow to each nasal prong. These devices have worked well for gas flows of between 0 to 5 liters per minute and have been well received by patients over the last 30 years. With patient interfaces such as nasal cannulae the stability of the nasal prongs on the face is very important, as movement of the prongs within the nares can cause severe irritation.
The new application of Humidified High Flow Nasal Cannula (HHFNC) extended therapies generally result in a nasal cannula reaching temperatures in excess of 35 degrees C. and flow rates of up to approximately 10 liters per minute for infants, up to approximately 20 liters per minute for pediatric applications and up to approximately 60 liters per minute (for adults).
Supplementary oxygen (if required) is generally supplied as a dry gas, but it is known to be beneficial to either heat and/or humidify gases before delivering them for breathing by a patient.
It is also known to be beneficial and therapeutic to supply an individual with a sufficient amount of respiratory airway pressure in order to maintain a minimum level of air volume in the lungs. Hence, the application of such sufficient pressure, called continuous positive airway pressure (CPAP), has been found to be advantageous in maintaining a minimum air volume or lung pressure when an individual is spontaneously breathing. CPAP can be supplied through nasal attachment devices, face masks, or endotracheal devices.
In the above therapies, breathing gases inhaled by a patient are preferably delivered in a condition having humidity near saturation level and at close to body temperature (usually at a temperature between 33° C. and 37° C.). Condensation or rain-out can form on the inside surfaces of the inspiratory breathing tube as the high humidity breathing gases cool and/or come into contact with the relatively cooler breathing tube surface. Condensate forming in a breathing tube can pool within the tube and be breathed or inhaled by a patient and may lead to coughing fits, choking or other discomfort. For neonatal applications in particular, mobile condensate is especially detrimental, and it is desirable to reduce mobile condensate as much as possible. Condensate within a breathing tube may also interfere with the performance of connected equipment and ancillary devices, filters and/or various sensors.
Attempts have been made to reduce the adverse effects of mobile condensate by either reducing the level of condensation forming, or providing collection points for draining condensed liquid from the tubing component. Reducing the condensation or rain-out forming has generally been achieved by maintaining or elevating the temperature above the dew point temperature of the breathing gas. This temperature is typically maintained by a heater wire arranged within the breathing tube (as shown in FIG. 1) in the path of flowing breathing gases, although the rain-out performance of these breathing tubes often may not be complete due to a number of factors. With reference to FIG. 1, a typical heated medical corrugated breathing tube 1 comprises an inner tube, and an outer tube and includes end connector fittings 2,3 of a standard type (moulded plastic) according to the intended use of the medical tubing and may incorporate an internal medical taper for example. The end connectors 2,3 may also include additional ports for receiving sensors and the like. End connector 3 (humidifier end) also includes a connection (not shown) for delivering power to the heater wire 5. Breathing tube 1, comprises one corrugated tube 115 within another corrugated tube 116, defining an insulation space between the tubes to improve rain-out performance.
Particularly, in ‘single use’ or short term use applications such as typically found in a hospital environment, the manufacturing cost of breathing tubes is especially important. It is highly desirable to even further reduce or eliminate mobile condensate, while preferably also maintaining a low production cost.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.